Oil leakage recycler

ABSTRACT

This invention relates to a pneumatically controlled hydraulically actuated brake apparatus that has a hydraulic fluid reservoir from which hydraulic fluid is supplied via a check valve to the cylinder of a hydraulic fluid motor, movement of the piston of which in one direction forces hydraulic fluid under pressure to a brake applying piston to effect a brake application. Each of these pistons is provided with piston seal members past which a limited quantity of hydraulic fluid in the form of leakage flows to a chamber at one side of the brake applying piston from which chamber this hydraulic fluid is returned to the hydraulic fluid reservoir for recycling.

United States Patent 1191 1111 3,913,328

Shaffer 1 Oct. 21, 1975 OIL LEAKAGE RECYCLER 4 Primary Examiner-Martin P, Schwadron l t l h if [75] nven 0r Ronad J S 3 er pmsburgh Pa Assistant Examiner-H, Burks, Sr. Assigneel Westinghouse Brake mp y, Attorney, Agent. or Firm-W. F, Poore', R. W.

Wilmerding, Pa. Mclntire, Jr

{22] Filed: July 10, 1974 57 ABSTRACT [21] Appl. No; 487,127 y This invention relates to a pneumatically controlled hydraulically actuated brake apparatus that has a hy- [52] Cl "601592; 188/53 R draulic fluid reservoir from which hydraulic fluid is 3 Cl Flsb 7/00 supplied via a check valve to the cylinder of a hydrau [58] held of Search 60535 592? lic fluid motor, movement of the piston of which in 188/52, 153 R, 196 A one direction forces hydraulic fluid under pressure to a brake applying piston to effect a brake application. [56] References C'ted Each of these pistons is provided with piston seal UNITED STATES PATENTS members past which a limited quantity of hydraulic 2,058,063 l0/l936 Cox 60/585 x fluid in the form 0f leakage flows to a Chamber at one 2,585,389 2/l952 Kehrl 60/572 Side of the brake applying piston from which chamber 2,827.766 3/1958 Huffordm, 60/560 this hydraulic fluid is returned to the hydraulic fluid 3,107,624 10/1963 Williams 60/592 X reservoir for recycling. 3,199.415 8/1965 Stanton et al... 60/592 x i G 3,200,596 8/[965 OiSOn et al 60/560 11 Claims 3 Drawmg Flgllres gz-s U.S. Patent 00:. 21, 1975 Sheet 1 of 2 3,913,328

PRIOR ART TO HYDRAULIC FLUID MOTOR US. Patent Oct. 21, 1975 Sheet 2 of2 3,913,328

ll ill 01L LEAKAGE RECYCLER BACKGROUND OF THE INVENTION In U.S. Pat. No. 3,837,443 issued Sept. 24, 1974 to Quentin T. Clemmons et al., and assigned to the assignee of the present application, there is shown and described a pneumatically controlled hydraulically actuated brake apparatus that embodies therein two seal-member-carrying pistons each of which, while a brake application is in effect, is subject on one side thereof to hydraulic fluid the pressure of which is of such magnitude as to cause an undesirable amount of leakage of the hydraulic fluid from the one side of these pistons past these seal members to the other side and thence to the exterior of the brake apparatus to cause contamination of the surrounding area.

Accordingly, it is the general purpose of this invention to provide a novel automatically operable means for effecting the return and recycling of the hydraulic fluid that leaks past the sealing rings carried by the pistons embodied in a pneumatically controlled hydraulically actuated brake apparatus and subject on one side to hydraulic fluid at a substantial pressure.

SUMMARY OF THE INVENTION According to the present invention, there is provided in a pneumatically controlled hydraulically actuated brake apparatus that includes a hydraulic fluid reservoir and two seal-member-carrying pistons subject on one side to hydraulic fluid at a substantial pressure, suitable conduits through which any hydraulic fluid that may leak from one side of the pistons past the seal members carried thereby to the other side is forced under pressure to return to the fluid reservoir for recycling or resupply therefrom to the one side of the pistons.

In the accompanying drawing:

FIG. 1 is a vertical sectional view of a presently known hydro-pneumatic converter device for supplying hydraulic fluid under pressure to a hydraulic brake applying piston.

FIG. 2 is a verticle sectional view of a pneumatically controlled hydraulically actuated brake apparatus embodying the invention.

FIG. 3 is a horizontal sectional view of the lower end of the guide member taken along sectional lines 33.

DESCRIPTION A conventional hydro-pneumatic converter device 1 is shown in FIG. 1 of the drawings for supplying hydraulic fluid under pressure to any suitable brake applying hydraulic fluid motor (not shown).

The construction and operation of the converter device 1 shown in FIG. 1 of the drawings may be substantially the same as that of the hydro-pneumatic converter device 13 shown and described in the abovementioned U.S. Pat. No. 3,837,443. Therefore, a detailed description of the converter device 1 is deemed unnecessary.

Briefly, however, the converter device 1 comprises a diaphragm 2 the inner periphery of which is clamped between a diaphragm follower 3 and a diaphragm follower plate 4 secured thereto by a plurality of cap screws 5 two of which appear in FIG. 1.

Formed integral with the diaphragm follower 3 is a guide stem 6 the lower end of which is slidably disposed in a bore 7 provided therefor in a casing section 8 that constitutes one of a pair of casing sections that form a sectionalized casing of the converter device 1.

As shown in FIG. 1, the interior of the bore 7 below the end of the stem 6 constitutes a chamber 9 that is supplied with hydraulic fluid from a hydraulic fluid reservoir 10 via a valve element 11 when unseated from a valve seat 12 in the manner explained in the abovementioned patent. In order to inhibit flow of hydraulic fluid from the chamber 9 to a chamber 13 upon downward movement of the guide stem 6, which constitutes a hydraulic piston, in response to the supply ofa pneumatic fluid under pressure to a chamber 14 above the diaphragm 2 via a passageway 15, the guide stem 6 is provided with a suitable seal member 16.

It has been found in actual practice that even when the best obtainable seal members are used, a limited amount of hydraulic fluid flows from the chamber 9 past the seal member 16 to the chamber 13 each time a brake application is effected. It can be seen from FIG. I that hydraulic fluid or liquid which flows from the chamber 9 past the seal member 16 to the chamber I3 may flow from this chamber 13 to the exterior of the converter 1 via an insect excluder device 17. It is apparent that this hydraulic fluid or liquid that flows past the insect excluder device 17 would contaminate the surrounding area thus creating an undesirable condition. Furthermore, this hydraulic fluid is lost and must be replaced by a like quantity of hydraulic fluid from the hydraulic fluid reservoir 10 which heretofore has been provided with a pair of sight glasses or observation windows 18 and 19 located one above the other in order to inform an observer when this reservoir is full of hydraulic fluid and when substantially empty.

There is shown in FIG. 2 of the drawings a pneumatically controlled hydraulically actuated brake converter device 20 embodying therein the present invention.

As shown in FIG. 2, the converter device 20 has a sectionalized casing comprising three casing sections 21. 22 and 23 secured together by any suitable means (not shown).

The casing section 21 is in the form of two opposed cup-shaped members separated by a wall 24. The upper cup-shaped member of this casing section 21 is closed by an upper cover member 25 that is secured thereto by a plurality of cap screws 26 two of which appear in FIG. 2. Thus, the upper cup-shaped member of the casing section 21 and the cover member 25 cooperate to form a hydraulic fluid reservoir 27 that may be filled with oil or some other suitable hydraulic fluid or liquid through a vented filling cap 28 screw-threaded into the cover member 25.

As shown in FIG. 2, the outer periphery of a diaphragm 29 is clamped between the casing sections 21 and 22, and the inner periphery of this diaphragm is clamped between a diaphragm follower 30 and a diaphragm follower plate 31 that is secured to this follower 30 by a plurality of cap screws 32 that pass through smooth bores provided therefor in the plate 31 and have screw-threaded engagement with coaxial screw-threaded bottomed bores in this follower 30.

The diaphragm 29 together with the follower 30 and follower plate 31 cooperate with the casing sections 21 and 22 to form on the respective opposite sides of the diaphragm 29 a pair of chambers 33 and 34. Pneumatic fluid under pressure may be supplied to the chamber 34 via a passageway and correspondingly numbered pipe 35 that is connected to such as the brake cylinder port of the usual brake control valve device (not shown) of the air brake equipment on railway vehicles under the control of the operator or locomotive engineer.

Formed integral with one side of the diaphragm follower 30 is a master hydraulic piston 36 the lower end of which is received in a bore 37 provided therefore in the casing section 22.

A spring 38 disposed about the piston 36 and interposed between the diaphragm follower 30 and the cas ing section 22 serves to yieldingly bias diaphragm 29 and piston 36 in a brake releasing direction to the position in which they are shown in FIG. 2. In this position the upper end of the diaphragm follower 30 abuts an annular stop 39 formed on the lower side of the wall 24.

As shown in FIG. 2, the piston 36 is provided with a bore 40 and two coaxial counterbores 41 and 42, the counterbore 41 extending through the diaphragm follower 30 to the upper side thereof and the counterbore 42 extending through the piston 36 to the lower end thereof. A tapered valve seat 43 is formed between the lower end of the bore 40 and the upper end of the counterbore 42 for a poppet-type valve 44 formed at the upper end of a cylindrical member 45 slidably mounted in the counterbore 42.

A snap ring 46 is inserted in a groove formed in the wall surface of the counterbore 42 and a spring 47 is interposed between this snap ring 46 and the cylindri cal member 45 for biasing an O-ring seal 48 carried by the valve 44 into seating contact with the valve seat 43 upon initial downward movement ofthe piston 36 from the position shown in FIG. 2.

Adjacent the lower end thereof the hydraulic piston 36 is provided with a peripheral annular groove in which is disposed a seal member 49 the purpose of which is to inhibit flow of hydraulic fluid under pressure from a chamber 50 below the piston 36 to the chamber 34 via the small clearance space between the wall surface of the bore 37 and the peripheral surface of the piston 36 that is necessary to provide for a sliding fit between this piston 36 and the wall surface of the bore 37.

As can be seen from FIG. 2, formed integral with the lower side ofthe wall 24 and surrounded by the annular stop 39 is a guide member 51 that extends into the counterbore 41 in the hydraulic piston 36. Adjacent its lower end, the guide member 51 is provided with a peripheral annular groove in which is carried a seal member 52 the purpose of which is to prevent leakage of pneumatic fluid under pressure from the chamber 34 to the bottom of the counterbore 41 and thence via the bore 40 and past valve 44 to the chamber 50 which is filled with hydraulic fluid. Furthermore. seal member 52 prevents leakage of the hydraulic fluid from the bottom of the counterbore 41 into the chamber 34.

Extending through the wall 24 and into the guide member 51 is a bottomed bore 53 the upper end of this bottomed bore being surrounded by a cup-shaped filter 54 that is disposed in the hydraulic fluid reservoir 27 and is constructed of, for example, screen wire. The filter 54 is provided with an outturned flange through which extend a pair of screws 55 that have screwthreaded engagement with screw-threaded bottomed bores provided therefor in the wall 24.

Extending upward from the lower end of the guide member 51 are four arcuately-spaced bottomed bores 56 that intersect the bottomed bore 53, as shown in FIG. 3 of the drawings, it being noted that the axes of these bottomed bores 56 are parallel to the axis of the bottomed bore 53. These bores 53 and 56 provide for the flow of hydraulic fluid from the reservoir 27 to the chamber 50 subsequent to the valve 44 being unseated from its seat 43 by the lower end of the guide member 51 abutting a stem 57 integral with the valve 44 and thereafter unseating this valve 44 as the hydraulic piston 36, diaphragm follower 30 and diaphragm 29 are moved upward by the spring 38 to the position shown in FIG. 2 in response to the release of pneumatic fluid under pressure from the chamber 34 via the passageway and pipe 35 and the usual brake control valve device on the vehicle upon return of this valve device to its brake release position.

As shown in FIG. 2 of the drawings, the casing section 23 is provided with a pair of parallel spaced-apart bushed bracket members 58 and 59 to enable the converter device 20 to be secured to a railway vehicle.

Furthermore, the casing section 23 is provided with a bottomed bore 60 into the right-hand end of which, as viewed in FIG. 2, opens one end of a passageway 61 that extends through the casing section 23 and at its opposite end opens into the chamber 50.

Slidably mounted in the bottomed bore 60 is a piston 62 that has formed integral therewith a piston rod 63 that extends through a bore 64 provided therefor in a lower cover member 65 that is secured to the left-hand end of the casing section 23, as viewed in FIG. 2, by any suitable means (not shown).

Adjacent its left-hand end, the piston rod 63 is provided with a bore 66 into which is pressed a wear bushing 67 to enable the piston rod 63 to be operatively connected by a linkage (not shown) to such as, for example, a disc brake or any other device that may be operated by the converter device 20.

Extending through the piston 62 and into the piston rod 63 is a tapered cavity 68 and a tapered coaxial counterbore 69. The purpose in making this cavity 68 and counterbore 69 tapered is to enable the escape of air bubbles that may become entrapped in the hydraulic fluid that is supplied from the chamber 50 to this cavity and counterbore and a chamber 70 formed by the cooperative relationship of the piston 62 and the casing section 23 via the passageway 61.

In order to permit drainage of hydraulic fluid from the reservoir 27 and chambers 50 and 70 when making repairs such as replacing worn parts, the casing section 23 is provided with a bore 71 and a coaxial screwthreaded counterbore 72 for receiving a removable screw-threaded plug 73.

As shown in FIG. 2, the periphery of the piston 62 is provided with an annular groove in which is disposed a seal member 74 to inhibit flow of hydraulic fluid under pressure from the chamber 70 into that portion of the bottomed bore 60 on the left-hand side of this piston 62.

As hereinbefore stated, even though the best obtainable seal members are used for the seal members 49 and 74, in actual practice when these seal members are subject to hydraulic fluid at a substantial pressure, a limited amount of hydraulic fluid or liquid will leak therepast. Accordingly, the converter device 20 shown in FIG. 2 of the drawings is provided with means new to be described for returning the hydraulic fluid or liquid that leaks past the seal members 49 and 74 to the hydraulic fluid reservoir 27 in order that this fluid may not be lost but recycled or reused.

As shown in FIG. 2, a passageway 75 extends substantially vertically through the casing sections 22 and 23. This passageway 75 opens at its upper end into the chamber 33 and at its lower end at the wall surface of the bottomed bore 60 adjacent the left-hand end thereof. Accordingly, this passageway 75 provides a conduit through which the hydraulic fluid that may leak past the seal member 49 into the chamber 33 may be conveyed or drained from this chamber into that portion of the bottomed bore 60 at the left-hand side of the piston 62.

As can be seen from FIG. 2, opening at the wall surface of the bottomed bore 60 adjacent the left-hand end thereof and diametrically opposite the opening of the passageway 75 at the wall surface of this bottomed bore 60, is one end of a passageway 76 that extends through the casing sections 23, 22, and 21 and the top cover member 25 and at its opposite end opens at a surface 77 formed on the lower side of this cover member 25, it being noted that this surface 77 is disposed a short distance above the surface of the hydraulic fluid in the reservoir 27.

it has been found in actual practice that the maximum cross sectional area of the passageway 76 should not exceed 0.0123 square inches for the reason that hydraulic fluid or liquid, as hereinafter explained, is forced by pneumatic pressure from that portion of the bottomed bore 60 on the left-hand side of the piston 62 through this passageway 76 back into the hydraulic fluid reservoir 27. Due to the surface tension of this hydraulic fluid, if the cross sectional area of the passageway 76 is in excess of 0.0123 square inches, the pneumatic pressure would blow through the hydraulic fluid or liquid so that this hydraulic fluid would not be forced back into the reservoir 27 as desired.

OPERATION When a brake application is effected in the manner described in the hereinbefore-mentioned patent, hydraulic fluid or liquid under pressure is forced from the chamber 50 into the chamber 70 via the passageway 61 in response to the supply of pneumatic fluid under pressure to the chamber 34 to cause deflection of the diaphragm 29 and downward movement of diaphragm follower 30 and piston 36.

However, a limited amount of hydraulic fluid or liquid will flow from the chamber 50 past the seal member 49 carried by the piston 36 into the chamber 33, and from the chamber 70 past the seal member 74 carried by the piston 62 into that portion of the bottomed bore 60 on the left-hand side of the piston 62.

The above-mentioned deflection of the diaphragm 29 and downward movement of the diaphragm follower 30 is effective to decrease the volume of the chamber 33 which it will be noted has no vent to atmosphere. Consequently, as the volume of the chamber 33 is thus decreased, the pressure therein is increased. Therefore, after a small quantity of hydraulic fluid or liquid has accumulated in the chamber 33 as the result of flow thereto from the chamber 50 past the seal member 49 carried by the hydraulic piston 36, a subsequent deflection of the diaphragm 29 and downward movement of the diaphragm follower 30 increases the pressure in the chamber 33 so that this increase of pressure in the chamber 33 is effective to force the hydraulic fluid or liquid in this chamber therefrom and into the passageway 75 from whence it flows into that portion of the bottomed bore 60 at the left-hand side of the piston 62 where it is combined with the hydraulic fluid or liquid that is forced from the chamber 70 past seal member 74 carried by the piston 62 and into this portion of the bottomed bore 60.

It will be noted from FIG. 2 of the drawings that the wall surface of the bore 64 in the lower cover member 65 is provided with a pair of spacedapart annular grooves in which are disposed respectively seal members 78 and 79 that encircle the peripheral surface of the piston rod 63 to form a seal therewith. Consequently, as the piston 62 is moved in the direction of the left-hand by the supply of hydraulic fluid under pressure to the chamber to decrease the volume of that portion of the bottomed bore 60 on the left-hand side of the piston 62, the pressure in this volume will increase.

Accordingly, as the pressure in that portion of the bottomed bore 60 on the left-hand side ofthe piston 62 increases in response to the movement of this piston 62 in the direction of the left hand, this increase in pressure is effective to force the accumulated hydraulic fluid or liquid in the bottomed bore 60 on the left-hand side of the piston 62 into the passageway 76, and thence through this passageway, the cross sectional area of which is not in excess of 0.0123 square inches, and into the hydraulic fluid reservoir 27.

From the foregoing, it is seen that the hydraulic fluid or liquid that leaks past the seal member 49 carried by the piston 36 and the hydraulic fluid or liquid that leaks past the seal member 74 carried by the piston 62 is returned to the hydraulic fluid reservoir 27 for recycling.

Having now described the invention what I claim as new and desire to secure by Letters Patent, is:

1. In a pneumatically controlled hydraulically actuated brake apparatus comprising a plurality of casing sections certain of which are provided with bores, a pair of tandem arranged abutments one of which is movable in opposite directions in one of said bores responsively to the application and release of pneumatic pressure to one of two chambers formed on the respective opposite sides of the other of said abutments by the cooperative relationship of said other abutment and a pair of said casing sections, a hydraulic reservoir from which a hydraulic medium may be supplied to said one bore, a third abutment movable in another of said bores responsively to the hydraulic pressure established in one of two chambers formed on the respective opposite sides thereof by movement of said one abutment in one direction in said one bore, and seal means carried by each of said one and said third abutment to respectively inhibit flow of hydraulic medium from said one bore to the other one of said two chambers and from said one of said two chambers to the other chamber on the other side of said abutment, wherein the improvement comprises:

a. first conduit means connecting said first other chamber and said second other chamber, and

b. second conduit means connecting said second other chamber and the hydraulic reservoir,

c. said first and second conduits cooperating to effect the return to the hdyraulic reservoir any hydraulic medium leaking past each of said seal means.

2. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that movement of said other abutment ofsaid pair of tandem arranged abutments in one direction in response to the supply of pneumatic pressure to said one of said first two chambers is effective to decrease the volume of the other of said first two chambers thereby increasing the pressure therein to cause flow of hydraulic medium therefrom to the hydraulic reservoir via said first conduit means, said second other chamber and said second conduit means.

3. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that movement of said other abutment of said pair of tandem arranged abutments in one direction in response to the supply of pneumatic pressure to said one of said first two chambers is effective to decrease the volume of the other of said first two chambers thereby increasing the pressure therein to cause flow of hydraulic medium therefrom to said second other chambver via said first conduit means, and move ment of said third abutment in one direction in response to the supply of hydraulic pressure to said one of said second two chambers is effective to decrease the volume of the other of said second two chambers thereby increasing the pressure therein to cause flow of hydraulic medium therefrom to the hydraulic reservoir via said second conduit means.

4. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that the casing section having therein said another bore is provided with drain means for draining hydraulic medium from said one of said second two chambers.

5. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that the casing section having therein said another bore is provided with conduit means connecting said one and said another bores through which hydraulic medium under pressure is conveyed to said third abutment upon movement of said one of said pair of tandem arranged abutments in said one direction.

6. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim I, further characterized in that said first conduit means extends respectively through those casing sections having therein said one bore and said another bore.

7. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that said second conduit means ex tends through all of said plurality of casing sections.

8. ln a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that the hydraulic reservoir is formed in one of said plurality of casing sections.

9. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that the maximum cross sectional area of said second conduit means is 0.0123 square inches.

10. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 6, further characterized by seal means carried by one of those casing sections having therein said one bore and said another bore, said seal means being disposed in surrounding relation to said first conduit and interposed between said casing sections to prevent leakage of hydraulic medium from said first conduit.

H. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 7, further characterized by seal means carried by one of each two pair of adjacent casing sections of said plurality of casing sections, each of said seal means being disposed in surrounding relation to said second conduit means and interposed between the respective pair of adjacent casing sections to prevent leakage of hydraulic medium from said second conduit.

* e a: =o= 

1. In a pneumatically controlled hydraulically actuated brake apparatus comprising a plurality of casing sectIons certain of which are provided with bores, a pair of tandem arranged abutments one of which is movable in opposite directions in one of said bores responsively to the application and release of pneumatic pressure to one of two chambers formed on the respective opposite sides of the other of said abutments by the cooperative relationship of said other abutment and a pair of said casing sections, a hydraulic reservoir from which a hydraulic medium may be supplied to said one bore, a third abutment movable in another of said bores responsively to the hydraulic pressure established in one of two chambers formed on the respective opposite sides thereof by movement of said one abutment in one direction in said one bore, and seal means carried by each of said one and said third abutment to respectively inhibit flow of hydraulic medium from said one bore to the other one of said two chambers and from said one of said two chambers to the other chamber on the other side of said abutment, wherein the improvement comprises: a. first conduit means connecting said first other chamber and said second other chamber, and b. second conduit means connecting said second other chamber and the hydraulic reservoir, c. said first and second conduits cooperating to effect the return to the hdyraulic reservoir any hydraulic medium leaking past each of said seal means.
 2. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that movement of said other abutment of said pair of tandem arranged abutments in one direction in response to the supply of pneumatic pressure to said one of said first two chambers is effective to decrease the volume of the other of said first two chambers thereby increasing the pressure therein to cause flow of hydraulic medium therefrom to the hydraulic reservoir via said first conduit means, said second other chamber and said second conduit means.
 3. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that movement of said other abutment of said pair of tandem arranged abutments in one direction in response to the supply of pneumatic pressure to said one of said first two chambers is effective to decrease the volume of the other of said first two chambers thereby increasing the pressure therein to cause flow of hydraulic medium therefrom to said second other chambver via said first conduit means, and movement of said third abutment in one direction in response to the supply of hydraulic pressure to said one of said second two chambers is effective to decrease the volume of the other of said second two chambers thereby increasing the pressure therein to cause flow of hydraulic medium therefrom to the hydraulic reservoir via said second conduit means.
 4. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that the casing section having therein said another bore is provided with drain means for draining hydraulic medium from said one of said second two chambers.
 5. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that the casing section having therein said another bore is provided with conduit means connecting said one and said another bores through which hydraulic medium under pressure is conveyed to said third abutment upon movement of said one of said pair of tandem arranged abutments in said one direction.
 6. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that said first conduit means extends respectively through those casing sections having therein said one bore and said another bore.
 7. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that said second conduit means extends through all of said plurality of casing sections.
 8. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that the hydraulic reservoir is formed in one of said plurality of casing sections.
 9. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 1, further characterized in that the maximum cross sectional area of said second conduit means is 0.0123 square inches.
 10. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 6, further characterized by seal means carried by one of those casing sections having therein said one bore and said another bore, said seal means being disposed in surrounding relation to said first conduit and interposed between said casing sections to prevent leakage of hydraulic medium from said first conduit.
 11. In a pneumatically controlled hydraulically actuated brake apparatus, as recited in claim 7, further characterized by seal means carried by one of each two pair of adjacent casing sections of said plurality of casing sections, each of said seal means being disposed in surrounding relation to said second conduit means and interposed between the respective pair of adjacent casing sections to prevent leakage of hydraulic medium from said second conduit. 